Methods for the withdrawal of samples from liquid, powders, and gases have been known for a long time. The siphon procedure in various modifications is suitable for the simple sample withdrawal from liquids and solutions. The same method is also applicable to stable suspensions, dispersions, and emulsions. In contrast thereto, if mixtures of liquids with readily volatile compounds are involved, samples are withdrawn by way of valving arrangements, such as gate valves, etc., in a multistage procedure. A compilation of the most well-known methods can be found in Kolthoff: "Treatise on Analytical Chemistry, Part I, Volume I," pp. 81 et esq.
When taking samples from dispersions and/or emulsions under pressure, which are highly sensitive to mechanical stress as well as to pressure expansion, as they are formed, for example, in the emulsion polymerization of vinyl chloride, the method heretofore employed has been discharging, via valves, a very large amount of sample in a multistage operation as the only possible way of obtaining a representative sample. However, this method is likewise unsatisfactory, since in case of sensitive dispersions, the latter frequently become unstable in the valves and/or in the valve cocks in the sample-withdrawal device, thus clogging the valves. In such a case, it is then no longer possible to obtain additional samples. Furthermore, an exact determination of the content of the dissolved and/or emulsified, gaseous proportion is impossible when following the gate or charging valve procedure, since a partial phase separation into liquid and gas occurs before the final discharge of the sample through the valves. Still further, the gate valve method has the disadvantage that rather large amounts of samples must be withdrawn, since connecting conduits and valves must possess specific and usually large inside cross sections, so that high flow velocities and the attendant instability of the dispersion can be avoided. However, excessive quantities of a sample mean, in any case, a loss of material and, on the other hand, the operating personnel can be inconvenienced and/or endangered thereby, especially when vinyl-chloride-containing samples are involved.
Consequently, the present invention is concerned with a sample withdrawal system which avoids the aforedescribed disadvantages of the prior state of the art.